A switching node usually comprises peripheral devices PE (connection equipment for subscribers or lines), a central computer platform CP, a message distribution device MB and further central units (switching matrix SN, protocol terminating equipment CCNC (e.g. #7), backing storage MD, operating equipment NC). A corresponding configuration is illustrated in FIG. 1.
The peripheral devices perform essential switching tasks, usually in connection with the voice channels of the peripheral device. They therefore contain switching, operation and administrative programs, as well as equipment data information relating to line location, signaling, authorizations, call numbers, individual characteristics of trunk lines and subscriber lines, and also data information relating to the capacity level and the configuration of the peripheral device. The central computer platform serves for the coordinated control of connection establishment and cleardown, as well as for the responses to administrative and error-related configuration changes.
The peripheral devices are connected to one another and to the common central computer platform by means of the message distribution system. The further central system components make special functions available to the network system, e.g. for switching through the voice channels, processing the signaling protocols, realizing the operator interface, or for storing bulk data.
For fail-safety reasons, the central components of a network system are of redundant design (e.g. duplicated). Either it is not possible to design the peripheral devices to be redundant or, in the case of more stringent failure requirements (e.g. saving stable connections beyond the failure of a peripheral device), they may have redundancy.
If signaling data and voice data are routed in a disassociated fashion on separate paths, and if the peripheral devices have then only the task of protocol processing and/or conversion without physical termination of the voice channels, then the restrictions on the peripheral devices with respect to the resource pool and number of voice channels that can be terminated are removed. For this application the capacity of the peripheral device is determined by the performance of the processors, the size of the memory and the capacity of the message interface.
Since more than one direction must be provided for switching the voice through between a calling subscriber and any called subscriber, depending on the origin and destination, therefore, two different peripheral devices PE from the set of all peripheral devices are involved in a given connection establishment and cleardown. FIG. 2 shows such a case in its most general form.
The classical peripheral device terminates exactly the trunk lines for whose call processing it is responsible. There are usually peripheral devices for terminating n PCM30 links (e.g. n=4 for 120 trunk lines). If the voice is now routed outside the peripheral device, the limit to the physically predetermined maximum number of trunk lines that can be terminated becomes inapplicable. For this application, a peripheral device can if necessary process more than 120 connections simultaneously. This is the case for instance for IP-based Internet subscribers whose telephony service is handled by means of Voice over IP (VoIP) under the control of the switching center. Further possible examples are circuit-switched connections that need to be converted by means of a media gateway (MG) into packet-oriented connections under the control of switching centers functioning as media gateway controllers (MGC), or packet-based (e.g. IP-based) connections between two switching centers functioning as media gateway controllers (MGC).
Support of the basic call (call without features) is necessary in all the above-mentioned cases. For this purpose, the inter-exchange signaling (e.g. #7 protocol) or subscriber signaling (e.g. EDSS1) generated or expected by the peripheral devices must be converted to the standards (e.g. H.323) defined for IP-based connections before being forwarded to packet-based subscribers or remote MGCs. If necessary, a media gateway located in the connection path of the payload data must be additionally set. This is likewise packet-based (e.g. IP-based) and is performed by means of suitable protocols (e.g. MGCP, Megaco/H.248) by the media gateway controller.
The new tasks of controlling a media gateway and conversion to the world of Internet-adapted protocols are preferably allotted to new, partially centralized units of the switching center. Such partially centralized units are multifunctional computer platforms with commercially available hardware and operating system-oriented software, and with standardized interfaces (preferably Ethernet with TCP/UDP and IP, but also E1/T1 on the basis of PCM/SDH technology with HDLC/LAPD). Besides the aforesaid tasks, said computer platforms can handle a multiplicity of new tasks emerging from the evolution of the switching center into a call feature server. (For example Internet supplementary services such as click-to-dial (CtD)). The aforesaid commercial platforms are therefore the interfaces of the network system functioning as call feature server in the direction of the packet network/Internet (packet/IP-based subscribers, MGCs, MGs, gatekeepers, AAA servers etc.) and make available packet network/Internet-relevant functions of the network system.
The following technical problem therefore arises with respect to the integration of the aforesaid commercial platforms:
A multiplicity of requirements must be taken into account when integrating a platform in a network system by means of standardized interfaces using LAN, PCM and SDH technology:
For instance the multiplicity of peripheral devices of a switching center should have as direct communications access to the platform to be integrated as all central equipment of the switching center. This means that no message transfer should be performed via units outside the message distribution system. Likewise, the performance of the link should be adaptable at any time to the respective requirements of the applications (scalability), and the physical interfaces of the commercial platform should be economic in use in terms of a few, well-utilized physical interfaces. At the same time, it must be possible to link alien applications on separate physical paths (independence of applications with different requirements for message length and delay), to connect a plurality of commercial platforms at the same time (boost performance and support different interface configurations of the commercial platform), to trigger an alarm on failures of the link at any time (preserve reliability and the maintenance quality of a switching center), and part failures of the link must not lead to the loss of function (redundancy).
According to the prior art, a similar linking problem between a switching center and a service platform is solved within the framework of intelligent network (IN) concepts. In the latter the HW platform of the service control point (SCP) can be viewed as a platform to be linked to a switching center.
SCPs make intelligent network (IN) functionality available across switching centers which can be used in a high performance manner, in extreme cases even per basic call (e.g. call number conversion). SCPs are integrated in the usually #7-based, signaling network of conventional circuit-switched networks. They are consequently linked to the switching centers via standardized interfaces, and moreover satisfy the high availability requirements expected from conventional network systems.
In comparison with the technical problem to be solved in the present case, the insurmountable difficulties set out below arise. The SCP concept is therefore an unsuitable basis for the extension of conventional switching centers in the direction of packet-oriented switching functions.
For instance SCPs have only limited proprietary/manufacturer-specific capabilities for communicating with the equipment of the switching center since they are based on a fully defined standardized protocol (INAP/#7) without sufficient capacity to meet the needs of communication with sub-devices of a network system. Furthermore, they are superordinate units that do not just support a single switching center and are not therefore realized on an open commercial platform on which the switching sub-functions of a switching center can be freely implemented. In addition, SCPs support services, but not complex control operations of the network, such as control of media gateways (MGs) per control protocol (MGCP, Megagco) for example. SCPs are unable to communicate with the devices of the network system for controlling devices outside the switching center (MG setting). Finally, SCPs offer just as few protocol converter functions and capabilities for communicating with subscribers of the switching center as is required for the platform to be linked in the present case. At present SCPs are linked on the basis of time division multiplexing, but not via Ethernet.